In a mobile communications network, a voice service setup delay of a calling user equipment and a called user equipment is one of indicators extremely focused by both an operator and a terminal user, where the voice service setup delay mainly refers to a difference between a time at which the calling user equipment initiates a call request and a time at which the calling user equipment receives ringing information.
In an existing mobile communications network, when a calling user equipment sets up a voice service with a called user equipment, a core network device needs to deliver an instruction to an access network device according to reported information of the access network device, and then the access network device sets up a signaling connection or a radio service bearer connection to the called user equipment based on the received instruction, and ringing information sent by the called user equipment also needs to be first uploaded to the core network device by using the access network device, and then delivered by the core network device to the calling user equipment by using the access network device.
However, in an existing communications system, for information exchange in a process of setting up a voice service between a calling user equipment (UE) and a called UE, serial processing in an access network-core network-access network manner needs to be performed, so that a voice service setup delay is relatively long, which affects service experience of a user.